Visweshwar Ram Marthi

Email: viswesh [at]
Phone: 02025719229
Extn: 9229
Office: F204B
National Centre for Radio Astrophysics
Tata Institute of Fundamental Research
Savitribai Phule Pune University Campus,
Pune 411 007
Maharashtra, INDIA

Main Research Areas: Statistical methods for 21-cm cosmology; Astronomy signal processing; The Warm Ionized Medium; Interstellar scintillation; Very Long Baseline Interferometry.



Visweshwar Ram Marthi earned his bachelor's and master's degrees in Electrical Engineering from the University of Madras and National Institute of Technology, Tiruchirappalli, respectively. Marthi had a brief stint in the telecommunication industry after a Masters in Electrical Engineering. For his Ph.D., he worked on the upgrade for the Ooty Radio Telescope, developing calibration and statistical methods for the redshifted 21-cm experiment. After his Ph.D., he worked as a postdoctoral fellow at the Canadian Institute of Theoretical Astrophysics at the University of Toronto, Canada. He returned to NCRA in September 2019, and is now a faculty member at NCRA.

Research description:

Marthi's current research focus is Scintillometry, i.e. using measurements and measurables of interstellar scintillation to study the properties of the interstellar medium (ISM). One of the preferred ways of studying the ISM is to use compact background objects to study radio wave propagation through the medium, to glean its physical properties. Radio propagation through plasma induces several observable effects such as dispersion, scattering, and scintillation. Although the three effects are distinct, they are intimately linked to one another. Traditionally, pulsars have been used to observe these effects and hence study the ISM. Additionally, active galactic nuclei (AGNs), although less popular, are often used as ISM probes. With the discovery of Fast Radio Bursts (FRBs) and the explosion in their numbers, these are now being used to study not just the ISM of the Milky Way, but also the properties of the ISM of the FRB host galaxy as well as the intergalactic medium. Using scintillation to study the phenomenon itself, as well as its applications to refine other measurements (such as, e.g., precisely solving pulsar binary orbits, measuring inclination angles, physical extent of emission regions, pulse reflex motion, extreme scattering and lensing, etc.) falls under Scintillometry. Marthi's scientific interests entail developing improved instrumentation to enable novel and niche science. He is therefore also working on Very Long Baseline Interferometry (VLBI) for the GMRT. Scintillometry can benefit greatly from VLBI, in terms of measuring the interstellar Green's function along different sightlines and the scattering geometry, i.e. whether isotropic or anisotropic. A census of pulsar scintillation can help build a 3D picture of the locations of scattering screens and explore the close and often less-than-intuitive connection between dispersion, scattering, and scintillation. As a longer-term research theme, he hopes to study the tiny-scale structure of the different phases of the ISM.

Selected publications:

1. Burst properties of the highly active FRB20201124A using uGMRT (V. R. Marthi et al. 2022, MNRAS, 509, 2209)

2. Scintillation time-scale measurement of the highly active FRB20201124A (R. A. Main, G. H. Hilmarsson, V. R. Marthi et al. 2022, MNRAS, 509, 3172)

3. Scintillation of PSR B1508+55 - the view from a 10 000-km baseline (V. R. Marthi et al. 2021, MNRAS, 506, 5160)

4. Detection of 15 bursts from the fast radio burst 180916.J0158+65 with the upgraded Giant Metrewave Radio Telescope (V. R. Marthi et al. 2022, MNRAS, 499, L16)

5. Non-linear redundancy calibration (V. R. Marthi and J. N. Chengalur 2014, MNRAS, 437, 524)